O_DIRECT support in 2.4.4?

From: Michael Susæg (Michael.Susag@fast.no)
Date: Fri Apr 27 2001 - 12:08:41 EDT

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    We have tested the rawio and o_direct patches from Andrea Arcangeli
    with great success, and wondered if they will be part of the next
    kernel release, 2.4.4?

    So far we have tested these patches on four different systems.
    With the latest versions of these patches (rawio-6, o_direct-3)
    all systems works perfectly ok. Both with and without O_DIRECT
    enabled in big file operations.

    The O_DIRECT support really helps performance a lot
    for some types of applications. We happen to have such an
    application, and we would like to see O_DIRECT
    support in the kernel source in the near future.
     
    This would lift Linux to a new level in terms of disk performance
    for "self-caching" applications.

    A performance test we did on our application shows a huge
    improvement, upto 8 times better data read speed with direct-IO.
    With buffered IO, the CPU is doing caching most of the time.

    I attached a graph showing this performance win using O_DIRECT
    versus buffered IO. Each thread reads at a random offset a random
    amount of data from a big data set. The dataset is placed on
    a software RAID 0 with many disks. With that configuration
    we are able to fully utilize the 160 MB/s SCSI controllers. 

    -- 
Michael Susæg, M.Eng.             Mail:  Michael.Susag@fast.no
Software Engineer                 Web:   http://www.fast.no/
Fast Search & Transfer ASA        Phone: +47 21 60 12 27
P.O. Box 1677 Vika                Fax:   +47 21 60 12 01
NO-0120 Oslo, NORWAY

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